The present invention relates to a velocity control of a spindle motor which drives the rotation of a disk in an electronic device using a disk, and more particularly to a circuit for preventing an abnormal rotation.
Generally, a spindle motor is a motor to control the rotation of a disk used as a recording medium in a compact disk player (hereinafter referred to as "CD player") and applied devices thereof. Systems for controlling the velocity of the spindle motor at a constant linear velocity are used in such devices as a CD player, a CD-I, a CD-ROM, a CD-ROMXA, etc.
As for CD players, the spindle motor has an angular velocity of a certain range to maintain a constant linear velocity for the inner and outer circumferences of the disk. Also, since the constant linear velocity has a range of 1.2m/s to 1.4m/s, if the constant linear velocities during writing and reading are not the same, the data cannot be read properly. That is, the control of the linear velocity depends on the recorded data.
Conventionally, to control the spindle motor, the frequency and phase of a radio frequency (RF) signal read from an optical pickup are compared with a reference clock. Then, the phase difference is used as a control signal for a spindle servo, thereby controlling the velocity of its motor.
However, in the above case, when there is a vibration or a shock due to the outer environment, focusing is not correct. Accordingly, precise control of the linear velocity cannot be accomplished, so that the data recorded on the disk cannot be read properly. Then, a signal processor cannot make a phase-comparison, and accordingly the spindle motor may be speeding forward or backward in many cases. This is because the outer environment is not taken into account. Accordingly, a control circuit which can keep the angular velocity of the spindle motor within a constant range, even under abnormal conditions, is required to solve such a problem.